1. Field of the Invention
The present invention relates to a system for the treatment of waste paper, and, more particularly, to such a system including a pulping drum for the treatment of waste paper.
2. Description of the Related Art
In a first wastepaper pulping stage, as known, varied difibration machines can be used, for example pulpers, disintegrators and pulping drums. The pulper consists essentially of a loadable tub into which the wastepaper is filled, forming a more or less viscous watery suspension that fills the container up to a certain level. Contained within the filled area, for breakup and mixing, is a powered rotor. Such pulper requires constant agitation of a large liquid volume (about 95% to 85% water), which costs much energy. Unlike the pulper, a pulping drum consists substantially of a horizontal cylinder, which on part of its surface is mostly perforated and features mostly on its end faces ring-shaped bulkheads in order to prevent an undesirable escape of the stock. Mixed with water, the wastepaper is disintegrated in the pulping drum by heaving, sliding and dropping, i.e., movement of the stock ingredients relative to one another. With sorting perforations present in the drum shell, the suspended fiber stock is allowed to exit. Exemplary embodiments of such pulping drums are illustrated and described, e.g., in the German patent document 32 10 503.
Wastepaper treatment methods employing such or similar pulping drums, as known, have the advantage of a particularly sparing pulping, both in terms of sensitive fiber grades and undesirable additives to be retained in a screenable state. Part of the bargain, however, is the disadvantage that these pulping drums most favorably should be used only in conjunction with wastepaper grades of especially easy pulpability, meaning that these contain possibly no shares of paper grades that are difficult to pulp. The expert is quite familiar with the definitions of easy-to-pulp and difficult-to-pulp, with newsprint, e.g., being easy-to-pulp and "partly wet-strength," surface-treated and "wet-strength" paper grades being difficult-to-pulp. One may also speak of high or low pulpability. Stated as a measure for pulpability, e.g., may be specific work required during the pulping process in the pulper to generate a pumpable suspension. With newsprint, e.g., pulpability amounts to about 15-20 kWh/t and with liner or surface-treated papers up to 80 kWh/t. Methods employing pulping drums have for these reasons proven themselves particularly with so-called deinking material, i.e., imprinted sorted wastepaper grades which--as mentioned already--normally pulp easily.
When using drums nonetheless for grates of limited pulpability, a procedure according to the teaching, e.g., of EP 0 486 904 A1 may be chosen. According to it, the drum serves the soaking of the wastepaper. This is followed by a rough cleaning, and only thereafter is the stock pulped in its entirety, with considerable addition of pulping chemicals, in a further machine.
EP 0 218 738 proposes a method using two drums in series. The first drum serves only the pulping and mixing, and the second drum the screening of undesirable wastepaper ingredients.